Substorm particle injections - last update: 9 May 1997, 2030 UT (RR)

The sharp increases of energetic particle fluxes in the near-Earth tail, known as particle injections, are among the most important and well-known manifestations of magnetospheric substorms. Although being known since late 1960s (Arnoldy and Chan, 1969; Winckler, 1970), they are still not explained in a satisfactory way. They have been extensively studied using the geostationary and other spacecraft (e.g., Walker at al., 1976; Baker et al., 1982; Belian et al., 1978; Sauvaud and Winckler, 1980).

Some observations concernign the injections:

The main questions relating to the injections are the location and means of particle acceleration. It seems obvious that the dipolarization related induced electric fields play some role in the particle acceleration (Lezniak and Winckler, 1970). Also the inward, adiabatic drift may play role in some injection events. However, there is most likely more to it:

Particle acceleration and adiabatic earthward displacement may not always produce flux increases (Sergeev et al., 1998). The resulting flux variation is a compromise between the flux increase due to acceleration (depending on how soft the energy spectrum is) and the density of energetic particles at the point where they are taken from (if we have nothing, we will get nothing). If the initial flux is low and the energy spectrum flat, one may get a flux decrease instead of an increase. The drifting electron holes (DEHs) are an extreme example of this effect.

Finally, the strongest injections may be responsible for the storm effects (enhanced ring current). However, the connection between storms and substorms is not quite settled yet.


See also: